Ethylene-propylene elastomeric copolymers (EPR) and ethylene-propylene-non-conjugated diene terpolymer elastomers (EPDM) have been known and commercially available for many years. They possess a variety of inherently satisfactory properties as elastomers which has enabled them to find utility in many commercial areas. Among their satisfactory inherent properties are their resilience, ozone resistance and fatigue life after vulcanization, which would ordinarily render them well suited for use in tire sidewalls, especially in the upper sidewall area immediately adjacent to the tread where a very large amount of flexing is encountered in service. A further important requirement for an elastomer for use in tire sidewalls is good cured adhesion to adjacent rubber compounds of the tire, i.e. carcass compounds and tread compounds. EPDM is normally deficient in such cured adhesion. Accordingly, it is common practice to use blends of unsaturated elastomers (polybutadiene, natural rubber and the like) for sidewall compounds, containing appropriate antioxidants, antiozonants and waxes to confer the necessary long term protection on the sidewalls made therefrom. Such chemical additives, however, have a tendency to decay or migrate over time, and thus lose their effectiveness. An elastomeric polymer compound which inherently possessed the necessary degree of resistance to ozone, oxygen and heat would be a desirable replacement. EPDM rubbers inherently possess these properties, but suffer from the above mentioned deficiency of lack of cured adhesion.